W10L3 - Plant hormones

W10L3 - Plant hormones - Biol 5B: Organismal Biology Spring...

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1 Biol 5B: Organismal Biology Spring ’09 WEEK 10; Lecture 3 Plant hormones Plant hormones • Plant hormones help coordinate growth, development, and responses to stimuli Hormones are chemical signals that coordinate different parts of an organism Tropism : – Any response resulting in curvature of organs toward or away from a stimulus is called a tropism – Tropisms are often caused by hormones
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2 Discovery of hormones • In the late 1800s, Charles Darwin and his son Francis conducted experiments on phototropism , a plant’s response to light • They observed that a grass seedling could bend toward light only if the tip of the coleoptile was present • They postulated that a signal was transmitted from the tip to the elongating region RESULTS Control Light Illuminated side of coleoptile Shaded side of coleoptile
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3 RESULTS Light Tip removed Darwin and Darwin: phototropic response only when tip is illuminated Tip covered by opaque cap Tip covered by trans- parent cap Site of curvature covered by opaque shield RESULTS Light Boysen-Jensen: phototropic response when tip is separated by permeable barrier, but not with impermeable barrier Tip separated by gelatin (permeable) Tip separated by mica (impermeable)
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4 A survey of plant hormones • In general, hormones control plant
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W10L3 - Plant hormones - Biol 5B: Organismal Biology Spring...

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